In data communications systems generally, and particularly in wireless data communications systems such as cellular radio frequency (RF) and infrared systems, the control of the transmission activities within a cell can be either distributed or centralized. This control is important when the medium (e.g. radio or infrared) must be shared among the inhabitants of the cell. Sharing may be by time-multiplexing, frequency-multiplexing, or code-division multiplexing of various kinds. There may be resources associated with the cell in addition to the transmission medium: for example, attachment to a wired backbone network, storage, or locally administered identifiers.
In distributed control, inhabitants of the cell cooperate by executing an algorithm, usually common to all. An example is carrier-sense multiple-access (CSMA), where all cell inhabitants follow a conditional procedure before transmitting. A description of the principles of such CSMA protocols will be found in section 26-20 of Reference Data for Engineers, 7th edition, SAMS (1991).
In centralized control, one inhabitant of the cell (here called the base station) provides information to the other inhabitants (here called mobiles) to coordinate their use of cell resources. For example, the base station may allocate frequency channels to mobile stations, or may specify times at which a mobile station can transmit. An advantage of centralized control is that because the base station maintains precise knowledge about the allocation state of cell resources, it can optimize the use of those resources to a greater degree than can a distributed control algorithm.
The base station maintains explicit knowledge of the identity of mobile stations that require its services. Such knowledge is used for a number of reasons including: efficient addressing and explicitly directed transfer of information to mobile stations so that battery power can be conserved, bandwidth allocation, routing and handoff as stations move across cells, and effective network management and control of mobile stations.
The process by which a mobile station introduces itself to the base station of its choice is called registration. The mobile station registers with a base station that will be referred to as its owner. The owner base station is responsible for providing the mobile station with access to the communication system. The set of mobile stations owned by a base station is called a network cell.
U.S. Pat. No. 5,159,592 describes a method for managing communication between a wired network and mobile communication units in which a network entity, called global gateway, maintains a plurality of network addresses. In response to a request from a mobile communication unit, the global gateway assigns one network address to the requesting mobile unit. The global gateway also buffers and routes data being directed to an address corresponding to the assigned network address, to the mobile communication unit having the assigned address.
U.S. Pat. No. 4,797,948 describes a communication system having a communication channel for transmitting data between a base station and a plurality of mobile radio units, wherein each radio unit has a unique identification code (ID) and wherein transmission from each radio unit to the base station include the unit's ID Code. A method for identifying which units are within RF communication proximity of a base station comprises the steps of, 1) transmitting a range message, including a low ID code parameter and a high ID code parameter, from the base station over the channel to elicit a response from at least one of the radio units having an ID code between the low and high parameters, 2) storing in an ID list a signal representative of the respective ID code assigned to radio units responsive to the range message. These steps are repeated with different transmitted range messages until each of the radio units within RF proximity of the base station is appended to the ID list.
U.S. Pat. No. 5,123,029 describes a hybrid of controlled access and random access schemes using frequency hopping spread spectrum communication techniques, implemented in an indoor digital data radio communication system between mobile stations and a computer system. A hop in the frequency hopping spread spectrum communications system is subdivided into two intervals so that different media-access protocols can be used in each interval. The protocol uses a centralized control scheme in one interval and a decentralized scheme in the other.
Radio frequency propagation channel is characterized by the presence of specific propagation phenomenons such as black-out zones, capture effects or fading conditions. These characteristics, combined with;the need to handle mobile stations, constantly entering or quitting network cells, require that robust and dynamic registration and deregistration methods be used.